Just wanted to think about twitter for a minute. Twitter gets huge percentage of its hits from mobile and processing almost a billion SMS messages a month.
http://blog.twitter.com/2010/04/cloudhopping.html

They've also said that their blackberry app gets 8% of their new sign-ups:
http://www.readwriteweb.com/archives/just_the_facts_statistics_from_twitter_chirp.php